Parallel-axis gear differentials of the type used in automotive drivelines generally include a housing rotatively driven by the vehicle powertrain and a gearset supported in the housing which interconnects a pair of coaxial output shafts. The gearset typically includes a pair of side gears fixed to end portions of the output shafts and meshed pair sets of pinions respectively meshed with the side gears. The pinions are rotatably supported in longitudinal gear pockets formed in the housing. The gear pockets are circumferentially arranged to support the meshed sets of pinions for rotation about pinion axes that are parallel to the rotary axis shared by the side gears and the housing. A representative example of such a parallel-axis gear differential is shown in U.S. Pat. No. 5,711,737.
As is known, during high torque conditions the gear loading may cause the ends of the pinions to move radially (i.e., "end tipping") which, in turn, causes the pinions to aggressively engage the bearing wall surfaces of the gear pockets, thereby potentially degrading the durability of the differential. In addition, such tipping often results in misalignment of the gear contact surfaces which can detrimentally impact tooth life and the efficiency of the gearset. In an effort to improve pinion alignment stability in parallel-axis gear differentials, various alternative support structures have been proposed. For example, U.S. Pat. No. 5,658,214 discloses the use of bearing plates to support the opposite ends of the intermeshed pinion set. In an alternative arrangement, U.S. Pat. No. 5,785,624 discloses the use of a supporting disc at one end of each pinion which bears against a journal post of the other pinion to support the ends of the meshed pinion set. Furthermore, U.S. Pat. No. 5,730,679 teaches of journalling an end shaft portion of each pinion in a support hole formed in the end walls of the housing for minimizing pinion tipping.
In addition to the pinion support arrangements described above, some parallel-axis gear differentials are designed to permit limited movement of the pinions for increasing frictional resistance to speed differentiation. For example, U.S. Pat. Nos. 5,415,599, 5,433,673 and 5,462,497 each disclose a parallel-axis gear differential equipped with a movable gear mounting structure (i.e., pivotable toggles or pedestals) having bearing surfaces which act on the outer diameter surface of adjacent pinions to apply a frictional braking force thereon. In a further modified form, U.S. Pat. No. 5,443,431 shows a similar movable gear mounting structure mounted in a casing portion of the housing with friction wedges supported by the casing portion between adjacent meshed pairs of pinions for further increasing frictional resistance to differentiation. Finally, U.S. Pat. No. 3,375,736 teaches of a limited slip differential having support blocks aligned axially with the pinions. A coil spring is disposed therebetween for biasing the support blocks and pinions in opposite axial directions and into contact with a pair of laterally-spaced friction plates which, in turn, are fixed for rotation with the side gears, thereby providing a spring-biased limited slip function. Consequently, there remains a need in the differential art for a parallel-axis differential with an anti-tipping feature that improves pinion alignment stability in a simple and cost-effective manner.